Study finds surprising relationship between teeth and pregnancy outcomes

Humans have the highest prenatal growth rate of any primate in existence, but how this exceptional rate occurred has been a mystery until now. Leslea Hlusko, a scientist at the Centro Nacional de Investigación sobre la Evolución Humana (CENIEH), participated in a study led by Tesla Monson, a paleoanthropologist at Western Washington University (WWU) in the United States, looking at teeth, prenatal growth pregnancy rates and progress. This research unearthed a key piece of this puzzle in an unexpected place: the relative sizes of fossilized molars.

Teeth are indicators of what’s going on elsewhere in the body, and this study, published in the journal Proceedings of the National Academy of Sciences (PNAS)shows that they can be used as a map to help untangle the effects of the interaction of genetics and development, as well as to improve our understanding of the history of life in the past.

Tesla Monson and his team, which also includes Andrew Weitz of WWU’s Department of Environmental Science, scientists from the Berkeley Geochronology Center (USA) and CENIEH, studied fossils from the primate group that includes apes and Old World apes, as well as data compiled from fossilized molars and skull fragments from the Late Miocene to Plio-Pleistocene period, ranging from about six million to some 12,000 years ago.

The results indicate that hominids reached a prenatal growth rate that sets them apart from all other apes between a million and a half million years ago, long before the human species itself evolved (it between 300,000 and 200,000 years ago).

molars

Prenatal growth rate is closely related to endocranial volume and, surprisingly, to variation in molar proportions. “This shows that teeth can be an indicator of both prenatal growth rate and brain size, which is of particular importance to our ability to study the gestational development of our human ancestors, because dental remains are the most abundant parts in the fossil record,” says Hlusko.

This discovery of the relationship between molar proportions and prenatal growth rates has raised many new questions for evolutionary researchers, such as understanding the underlying genetic mechanisms. Another of the key questions is whether this is also found in other mammals.

“While I don’t think our humanity can be reduced to teeth alone, I do believe that some of it is recorded in our teeth. This work opens a window for studies of pregnancy and gestation. We can take dental material from ancestor humans and other fossil primates to find out what their pregnancies looked like,” Monson concludes.